Monday's Book: The Seville Communion by Arturo Perez-Reverte (trans. Sonia Soto) Harvill, pounds 10.99

Is nothing sacred? A hacker codenamed Vespers has penetrated the sophisticated security system of the Vatican and left a message on the Pope's personal computer. It begs the world's most powerful monarch to intervene to prevent the threatened demolition of Our Lady of Tears, a dilapidated Baroque church in Seville. Vespers claims the church has started to protect itself by killing those that threaten its existence. Orders filter through the hierarchy to Father Lorenzo Quart, elegant trouble- shooter of the Vatican Information Service, who is despatched to Seville to report.

The church, Quart discovers, is already doomed. An unholy alliance between the archbishop and a land-hungry bank has long since settled its fate. The vice-chairman of the bank, a dashing, designer-suited piranha, has delegated the resolution of minor problems to Seville's criminal fraternity. All that stands in the way of the church's destruction are an uncouth little parish priest and his curate, a widowed duchess and her beautiful daughter, an American nun, a dwindling congregation and - well, maybe - the church itself.

But who is Vespers? Were the two deaths in the church as accidental as the police believe? This is Seville, and even the questions are less straightforward than they seem. Hot, old and beautiful, the city is full of ghosts. Quart is haunted by his predecessors as Papal hard men, the crusading Knights Templar, and by unfinished business in his own past. And there's the duchess's long-dead aunt, a woman whom love drove mad and whose correspondence finds its way, a century later, to Quart's hotel room.

Nor are Quart's flesh-and-blood problems any easier to handle. The archbishop dislikes him. The old priest is obdurate, and the curate violent. Quart needs all his self-discipline to cope with the disturbing allure of the duchess's daughter, who is also, as it happens, the estranged wife of the predatory banker.

Quart is followed by a bogus lawyer, a retired bullfighter and an alcoholic flamenco singer. As the plot twists through the labyrinthine streets of Seville, he becomes increasingly uncertain which mystery he is attempting to solve. The real enigmas lie within: the dark secrets of his own heart and the nature of faith in the modern world.

Classy and brimming with panache, The Seville Communion is much more than a witty, well-constructed entertainment, just as Quart is no ordinary detective but a sexy soldier of Christ armed with a gold card and a laptop computer. As The Flanders Panel and The Dumas Club have already shown, Perez-Reverte has a refreshing ability to escape from the formulae of crime fiction without sacrificing the genre's reader-friendly virtues. He uses this crime novel to launch an ambitious investigation which is as much metaphysical and theological as forensic. Yet he always plays by rules: only in the very last sentence do we learn the identity of the murderer.